I have 2 alpha 6's with 2 eminence asd1001 compression horns. I used an eminence pxb3k5 2 way crossover. I put the crossover in the cans with the alpha 6's. The alphas rms at 100 watts, the compression horns rms at 50 watts. I am running the whole sysem in parallel. So I show my amp a 4 ohm load. I am pushing about 330 watts rms at 4 ohms. It sounds a ton better for the rider and it is not as loud in the boat as my 2 boston pros I had on the tower last year. It really projects the sound far. Here is a pic of my tower speakers.
Feel free to ask any more questions. It's not that hard to tune the system correctly. Just make sure you have your High Pass crossover on your amp set to about right hz for what you go with, and also get the best crossover for your system. I got all my stuff from www.partsexpress.com